Motor

ABSTRACT

A motor that can prevent damages on the fluid dynamic bearing. A ball is press-fitted into the end surface of the shaft body, and the ball is disposed in such a manner that the tip portion of the ball comes to the higher position with respect to the end surface of the annular body. When the shaft is at rest, the ball abuts against the upper surface of the counter plate, and the end surface of the annular body is brought into a state of being raised from the upper surface of the counter plate, so that the situation in which the end surface of the annular body and the upper surface of the counter plate are brought into almost fully touch each other can be avoided. Therefore, when the operation is started, the circulation speed of a fluid increases and a fluid layer is quickly formed. As a consequent, the fluid circularity blocking action, which could be occurred in the relate art, is avoided, and generation of scratch caused by starting rotation in the tightly sticked state can be positively prevented.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor for driving magnetic disks suchas a spindle motor used in the hard disk drive device of the computer.

2. Description of the Related Art

Recently, the field of the hard disk drive device has been making steadyprogress in increasing capacity thereof. In order to optimize such aprogress in increasing capacity, there is a growing need for higherrotational speed for the motor used in the hard disk drive device. As abearing for such a motor, a ball bearing has been generally used so far.However, in order to optimize the need for higher rotational speed,application of fluid dynamic bearings has been introduced.

As an example of the motor used in the hard disk drive device andcomprising a fluid dynamic bearing, there is shown in FIG. 20 a spindlemotor for driving magnetic disks. The spindle motor 1 for drivingmagnetic disks (hereinafter, referred to as a spindle motor) is providedwith a magnet 5 on the rotor 4 so as to face toward the stator 3provided on the flange 2.

The flange 2 generally comprises a flange body 6 for holding the stator3, and a sleeve 7 to be press-fitted into the hole (sleeve fitting hole6 a) formed on the flange body 6.

The sleeve 7 generally comprises a cylindrical sleeve body 9 and adisk-shaped counter plate 11.

The sleeve body 9 comprises a hole (no reference numeral is assigned)extending from one side (the upper side in FIG. 20) to the other side(the lower side in FIG. 20) for inserting a shaft 12 therein, and thehole is constructed of a hole formed on one side (hereinafter, referredto as a sleeve hole) 7 a and an annular stepped portion 8 formedconcentrically and in communication with the sleeve hole 7 a via a step.

As shown in FIG. 21 and FIG. 22, the annular stepped portion 8 comprisesan annular hole 8 a having a larger inner diameter in comparison withthe sleeve hole 7 a and formed in communication with the sleeve hole 7 avia a step (hereinafter, referred to as a medium diameter annular hole),and an annular hole having a larger inner diameter in comparison withthe medium diameter annular hole 8 a and formed in communication withthe medium diameter annular hole 8 a via a step hereinafter, referred toas large diameter annular hole). The large diameter annular hole 8 bopens at one end (the lower side in FIG. 21) of the sleeve body 9. Thecounter plate 11 is disposed at the large diameter annular hole 8 b, andthe counter plate 11 and the sleeve body 9 are hermetically connected bywelding or the like.

The shaft 12 comprises a shaft body 12 a, and an annular body 10 fittedon one end (the lower portion in FIG. 20) of the shaft body 12 a. Theannular body 10 of the shaft 12 is disposed in the medium diameterannular hole 8 a and the shaft body 12 a of the shaft 12 is insertedinto the sleeve hole 7 a.

As described above, the annular body 10 of the shaft 12 is disposed inthe medium annular hole 8 a and the shaft body 12 a of the shaft 12 isinserted into the sleeve hole 7 a, and the sleeve 7 constitutes a fluiddynamic bearing 13 with the shaft 12. Though oil 14 is generally used asa fluid for the fluid dynamic bearing 13, it may be constructed to usegas such as air.

In other words, a plurality of rows of groves 15 are formed on the innerwall (sleeve hole 7 a) of the sleeve body 9, and a plurality of rows ofgrooves (not shown) are formed on the end portion of the annular body 10that touches the stepped wall surface of the medium annular hole 8 a ofthe sleeve body 9 and the portion of the upper surface of the counterplate 11 that touches the annular body 10. Oil 14 is filled and reservedin the gap between the sleeve 7 including the grooves 15 and the shaft12, and in the grooves that are not shown in the figure. The innerperipheral surface of the annular body 10 is formed with a fluidcirculating groove 10 a so as to facilitate circulation of the fluid.The annular body 10 slightly projects toward the counter plate 11 withrespect to the shaft 12, so as to facilitate inflow and outflow of fluidfrom and to the fluid circulating groove 10 a.

The annular body 10 of the shaft 12 is disposed at the medium diameterannular hole 8 a, that is, between the wall surface of the mediumdiameter annular hole 8 a that faces in the axial direction (the upperside in FIG. 20) and the counter plate 11, so that the axial movement(vertical movement in FIG. 20) of the shaft 12 is controlled via theannular body 10.

The dynamic pressure generated by the pumping action in association withrotation of the shaft 12 forces a fluid layer to be formed between thesleeve 7 and the shaft 12, and the shaft 12 that touched the counterplate 11 as shown in FIG. 21 during the rest time rises from the counterplate 11 as shown in FIG. 22, so that the shaft 12 can rotate withrespect to the sleeve 7 via the fluid layer. The fluid dynamic bearing13 forms a fluid layer by the dynamic pressure and forms a gap betweenthe shaft 12 and the counter plate 11 to support a thrust load of theshaft 12 as described above [in other words, the counter plate 11supports a thrust load applied downwardly of the shaft 12 (in thedirection of the arrow D in FIG. 20), and the ceiling wall of the mediumdiameter annular hole portion 8 a supports a thrust load appliedupwardly of the shaft 12 (annular body 10) (in the direction of thearrow U in FIG. 20)], and a radial load of the shaft 12 is supported bythe portion of the sleeve 7 where the sleeve hole 7 a is formed.

Referring now to FIG. 21 and FIG. 22, the operation of the fluid dynamicbearing of the related art will be described.

FIG. 22 shows a state in which the 12 is rotated and the dynamicpressure of a fluid is generated.

In FIG. 22, when the spindle motor 1 is actuated and the shaft 12 startsrotating, the dynamic pressure is generated and thus a fluid layer isformed in the gap formed between the inner diameter surface of thesleeve 7 that is a fixed body and the outer peripheral surface of theshaft 12 that is a rotating body, between the stepped end surface(annular stepped portion 8) of the sleeve 7 and the opposing end surfaceof the annual body 10, between the wall surface of the medium diameterannular hole 8 a of the sleeve 7 and the outer diameter surface of theannular body 10, and between the upper surface 11 a (inner end surface)of the counter plate 11 that is fitted into the sleeve 7 and the endsurface 10 b of the annular body 10 and the end surface 12 b of theshaft body 12 a, so that the rotating portion can rotate withouttouching the stationary portion, thereby forming a fluid dynamicbearing.

In FIG. 22, G07 designates an axial distance of the gap formed betweenthe end surface 10 b of the annular body 10 and the upper surface 11 aof the counter plate 11 when the rotor 4 (shaft 12) is rotated at aspecified rotational speed.

FIG. 21 shows that state of the end portion of the shaft when thespindle motor 1 is oriented in such a manner that the counter plate 11faces downward when the rotation of the shaft 12 is stopped and remainedat rest.

In FIG. 21, loads of the hub 32, the yolk 41, and the magnet 5 assembledto the shaft 12 shown in FIG. 20 are applied downward, and thus theshaft 12 on which the annular body 10 is fitted moves downward, wherebythe end surface 10 b of the annular body 10 touches the upper surface 11a of the counter plate 11 via a thin fluid layer. Since the fluid layerinterposed between the upper surface 11 a of the counter plate 11 andthe end surface 10 b of the annular body 10 is extremely thin, a gap G17between the upper surface 11 a of the counter plate 11 and the endsurface 10 b of the annular body 10 becomes extremely small value, orotherwise they may touch each other.

In the spindle motor 1, as shown in FIG. 20, when the shaft 12 isoriented in the vertical direction and disposed on the counter plate 11,a load is applied to the lower end of the shaft 12, and thus when animpact or vibrations is applied, the fluid layer on the contact surfaceis susceptible to mechanical damages such as breakage or scratch.

For example, when rotation of the shaft 12 is started, so-called fluidcircularity blocking action is effected because circulation of a fluidis slow due to narrow gap G17. As a consequent, the fluid layer cannotbe formed quickly, and thus the body of revolution (shaft 12) cannotrise quickly or sufficiently, which may result in difficulty inperforming the function of the fluid layer as a fluid dynamic bearing.In a state where the shaft 12 is not rotating, there is no rising actionon effected by the fluid dynamic pressure, and thus the lower endsurface of the shaft 12 (the end surface 10 b of the annular body 10)touches the upper surface 11 a of the counter plate 11 as shown in FIG.21, which results in scratch on both contact surfaces.

Especially, during transportation or handling, it is susceptible to alarge impact. In such a case, damages on the contact surface mayincrease and may cause failure in the performance of the apparatus.

SUMMARY OF THE INVENTION

In view of such circumstances, it is an object of the present inventionto provide a motor that can prevent damages to the fluid dynamicbearing.

A motor according to the first aspect of the present invention has arotating member supported on a stationary portion via a fluid dynamicbearing for supporting both of a thrust load and a radial load, andcomprises one or more projections provided on one of the opposinggenerally flat surfaces at the end of the shaft of the fluid dynamicbearing each as a separate unit, wherein the projections are capable ofabutting against the other surface when the rotating member is at rest.

Preferably, one of the surfaces is an end surface of the shaft providedon the rotating member and the other one of the surfaces is the portionon the surface of the stationary portion facing toward the end surfaceof the shaft, or one of the surfaces is the portion on the surface ofthe stationary portion facing toward the end surface of the shaft andthe other one of the surfaces is an end surface of the shaft.

A motor according to the second aspect of the present inventioncomprises a shaft fitted with an annular body on one end of the shaftbody, a rotating member supported on the stationary portion via a fluiddynamic bearing for supporting both of a thrust load and a radial load,and one or more projections provided on the end surface of the shaftbody each as a separate unit, wherein the projection is provided in sucha manner that the tip portion thereof comes to the position higher thanthe end surface of the annular body.

A motor according to the third aspect of the present invention comprisesa shaft fitted with an annular body on one end of the shaft body, arotating member supported on the stationary portion via a fluid dynamicbearing for supporting both of a thrust load and a radial load, and oneor more projections provided on the end surface of the annular body eachas a separate unit.

A motor according to the forth aspect of the present invention comprisesa shaft fitted with an annular body on one end of the shaft body, arotating member supported on the stationary portion via a fluid dynamicbearing for supporting both of a thrust load and a radial load, and oneor more projections provided on the portion on the surface of thestationary portion facing toward the end surface of the annular bodyeach as a separate unit.

A motor according to the fifth aspect of the present invention comprisesa shaft fitted with an annular body on one end of the shaft body, arotating member supported on the stationary portion via a fluid dynamicbearing for supporting both of a thrust load and a radial load, and oneor more projections provided on the portion on the surface of thestationary portion facing toward the end surface of the shaft each as aseparate unit, wherein the height of the projection from the mountedportion is larger than the distance from the end surface of the shaftbody to the end surface of the annular body.

Preferably, the projection is press-fitted into the member on which theprojection is to be provided.

Preferably, the projection has a spherical shape.

Preferably, the projection is formed of ceramic.

Preferably, the projection is a member made of a high hardness materialformed by a sputtering.

Preferably, the member is formed of a base member containing silicon orchromium as a component and a secondary member made of a high hardnessmaterial placed thereon, and both of the members are formed by thesputtering.

Preferably, the member made of a high hardness material is amorphouscarbon or DLC (Diamond-like Carbon).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing an embodiment of the presentinvention;

FIG. 2 is a cross sectional view showing a spindle motor shown in FIG. 1remained at rest;

FIG. 3 is a cross sectional view of the spindle motor shown in FIG. 1 inthe state of being rotated;

FIG. 4 is a cross sectional view explaining the setting of the height ofthe ball shown in FIG. 1;

FIG. 5 is a cross sectional view showing the second embodiment of thepresent invention;

FIG. 6 is a cross sectional view of the spindle motor according to thethird embodiment remained at rest;

FIG. 7 is a cross sectional view showing the spindle motor shown in FIG.6 in the state of being rotated;

FIG. 8 is a cross sectional view explaining the setting of the height ofthe ball shown in FIG. 6;

FIG. 9 is a cross sectional view explaining the setting of the height ofthe ball for the spindle motor according to the fourth embodiment of thepresent invention;

FIG. 10 is a cross sectional view explaining the setting of the ball forthe spindle motor according to the fifth embodiment;

FIG. 11 is a cross sectional view showing an example of the presentinvention in which a conical projection is provided on the shaft body;

FIG. 12 is a cross sectional view showing an example of the presentinvention in which a conical projection is provided an the counterplate;

FIG. 13 is a cross sectional view showing the six embodiment of thepresent invention;

FIG. 14 is a cross sectional view showing the seventh embodiment of thepresent invention.

FIG. 15 is a cross sectional view showing the eighth embodiment of thepresent invention.

FIG. 16 is a cross sectional view showing the ninth embodiment of thepresent invention.

FIG. 17 is a cross sectional view showing the tenth embodiment of thepresent invention.

FIG. 18 is a cross sectional view showing the eleventh embodiment of thepresent invention.

FIG. 19 is a cross sectional view showing the twelfth embodiment of thepresent invention.

FIG. 20 is a cross sectional view showing an example of the conventionalspindle motor;

FIG. 21 is a cross sectional view showing the spindle motor of FIG. 20at rest; and

FIG. 22 is a cross sectional view showing the spindle motor of FIG. 20in the state of being rotated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 to 3, a first embodiment of the presentinvention will be described. The first embodiment corresponds to thesecond aspect of the present invention.

The same parts as in FIGS. 20 to 22 are designated by the same referencenumerals and the description thereof will be omitted as appropriate.

In the spindle motor 1A (a spindle motor for driving magnetic disks), arotor 4 is provided with a magnet 5 facing toward the stator 3 providedon the flange 2 as shown in FIG. 1.

The flange 2 is generally constructed of a flange body 6 formed ofaluminum or of stainless material holding the stator 3, and a sleeve 7to be press-fitted into a hole (sleeve fitting hole 6 a) formed on theflange body 6.

The flange body 6 generally comprises a cylindrical central cylindricalportion 20 having the sleeve fitting hole 6 a, and a frame 21 providedon the proximal side of the central cylindrical portion 20 so as toextend radially outwardly.

The frame 21 generally comprises an annular base portion 22 integrallyextending from the central cylindrical portion 20, a cylindrical outerperipheral wall portion 23 extending upwardly from the outer peripheraledge of the base portion 22, and an extension 24 extending radiallyoutwardly from the upper end of the outer peripheral wall 23, and thereis provided an annular space 25 between the central cylindrical portion20 and the outer peripheral wall 23.

The stator 3 comprises a stator stack 27 and a coil 28 wound by thestator stack 27, and disposed in the annular space 25 with the statorstack 27 supported by the outer peripheral surface of the centralcylindrical portion 20. The coil 28 is connected to the outer circuitvia the connector 30 to which the outgoing line 29 is connected. In FIG.1, the reference numeral 31 designates a sealing member.

The rotor 4 generally comprises a hub 32 formed of aluminum or stainlessmaterials, and a shaft 12 fixed to the hub 32.

The hub 32 has a cup shaped configuration with three steps with theiropened sides down in such a manner that the diameters of whichsequentially increases from the top toward the bottom. Hereinafter,these cylindrical bodies are referred to as the first, the second, andthe third hub cylindrical bodies 32 a, 32 b, 32 c, in ascending orderfor the sake of convenience.

The shaft 12 is fitted to the hole 34 formed on the bottom of the firsthub cylindrical body 32 a.

A magnetic disk 36 is fitted on the outer peripheral surface of theouter peripheral wall 35 of the first hub cylindrical body 32 a, and thefirst hub cylindrical body 32 a is formed with a female screw 37 forfixing the cover for holding the magnetic disk 36 on the outerperipheral wall 35 thereof. The first hub cylindrical body 32 a isformed with a plurality of holes 39 on the outer peripheral wall 35along the circumference thereof, so that a balance weight 40 can beselectively mounted to these holes 39.

As shown in FIG. 1 and FIG. 2, a plurality of rows of grooves 15 areformed on the inner peripheral wall of the sleeve body 9 (sleeve hole 7a), and a plurality of rows of grooves (not shown) are formed on the endportion of the annular body 10 that touches the wall surface of theannular stepped portion 8 of the sleeve body 9, and the portion thattouches the annular body 10 of the counter plate 11. Oil 14 is filledand reserved in the gap between the sleeve 7 including the groves 15 andthe shaft 12, and in the grooves that are not shown in the figure. Inthis embodiment, the shaft 12 is constructed of a shaft body 12 a thatis a body of the shaft, and an annular body 10.

The dynamic pressure generated by the pumping action in association withrotation of the shaft 12 forces a fluid layer to be formed between thesleeve 7 and the shaft 12, whereby the shaft 12 rises with respect tothe counter plate 11 and the shaft 12 rotates with respect to the sleeve7 via a fluid layer as shown in FIG. 3. In other words, the fluiddynamic bearing 13 forms a fluid layer by the dynamic pressure asdescribed above to form a gap between the shaft 12 and the counter plate11 (stationary portion) to support a thrust load of the shaft 12 (inother words, the counter 11 supports a thrust load applied downwardly ofthe shaft 12 (in the direction of the arrow D in FIG. 1) and the ceilingwall of the medium diameter hole portion 8 a supports a thrust loadapplied upwardly of the shaft 12 (annular body 10) (in the direction ofthe arrow U in FIG. 1), and a radial load of the shaft 12 is supportedby the portion of the sleeve 7 where the sleeve hole 7 a is formed.

The inner peripheral surface of the annular body 10 is formed with oneor more fluid circulating groove 10 a so as to facilitate circulation ofthe fluid. The annular body 10 slightly projects toward the counterplate 11 with respect to the shaft 12, so as to facilitate inflow andoutflow of fluid from and to the fluid circulating groove 10 a. It isalso possible to provide the annular body 10 so as not to project towardthe counter plate 11 with respect to the shaft body 12 a to form a flatsurface (or to be flush with the shaft body 12 a).

The annular body 10 of the shaft 12 is disposed at the medium diameterannular hole 8 a, that is, between the wall surface of the mediumdiameter annular hole 8 a that faces in the axial direction (the upperside in FIG. 1) and the counter plate 11, so that the movement (verticalmovement in FIG. 1) of the shaft 12 is controlled via the annular body10.

The central position of the end surface 12 b of the shaft body 12 a ispress-fitted with a ball (projection) 51 formed from ceramic. The ball51 is provided in such a manner that the tip portion (not designated bythe reference numeral) comes to the position higher than the end surface10 b of the annular body 10.

The position to which the ball 51 is mounted is not limited to thecentral position of the end surface 12 b of the shaft body 12 a, but itmay be any positions other than the central position as far as it is onthe end surface 12 b of the shaft body 12 a. There may be provided aplurality of balls 51. When a plurality of balls 51 are provided, it ispreferably to arrange the plurality of balls 51 so that a load of theshaft 12 can be supported in a balanced manner.

The ball 51 is provided in such a manner that the tip portion thereofcomes to the position higher than the end surface 10 b of the annularbody 10. More specifically, the projection measurement h of the ball 51from the end surface 12 b of the shaft body 12 a or the height ht of theball 51 is determined as follows.

The distance G2, the distance G3, and the distance G0 shown in FIG. 4are determined as follows, and the projection measurement h or theheight ht of the ball 51 is determined so that the sum of the distanceG2 and the distance G3 is equal to the distance G0; (G2+G3=G0).

(1) The distance G2: The axial distance between the end surface 10 b ofthe annular body 10 and the upper surface 11 a of the counter plate 11when the tip portion of the ball 51 touches the upper portion 11 a ofthe counter plate 11 facing toward the shaft 12 with the shaft 12 (rotor4) remained at rest. FIG. 4 is a cross section taken when the shaft 12is being rotated, and the distance G2 shown in FIG. 4 is marked just forthe sake of convenience.

(2) The distance G3: The axial distance between the tip portion of theball 51 and the upper surface 11 a of the counter plate 11 when theshaft 12 is rotated at a specified rotational speed.

(3) The distance G0: The axial distance between the end surface 10 b ofthe annual body 10 and the upper surface 11 a of the counter plate 11when the shaft 12 is rotated at a specified rotational speed.

In this embodiment, a ball 51 is provided on the end surface 12 b of theshaft body 12 a in such a manner that the tip portion of the ball 51comes to the position higher than the end surface 10 b of the annualbody 10 as described above. In this arrangement, when the shaft 12 is atrest, the ball 51 abuts against the upper portion 11 a of the counterplate 11, and the end surface 10 b of the annual body 10 is brought intoa state of being raised from the upper surface 11 a of the counter plate11, so that the situation in which the end surface 10 b of the annularbody 10 and the upper surface 11 a of the counter plate 11 are broughtinto almost fully touch each other, which could be occurred in therelated art described above, can be avoided. Therefore, a specified gapis formed between the end surface 10 b of the annular body 10 and theupper surface 11 a of the counter plate 11, and thus the circulationspeed of a fluid is increased when rotation is started. As a consequent,a fluid layer is quickly formed and thus the shaft 12 rises quickly andsufficiently.

As described above, when the shaft 12 is at rest, the ball 51 abutsagainst the upper surface 11 a of the counter plate 11, and the endsurface 10 b of the annular body 10 is brought into a state of beingraised from the upper surface 11 a of the counter plate 11, and theshaft 12 is raised sufficiently and quickly. Therefore, a fluidcircularity blocking action caused by adhesion in the tightly stickedstate or by a small clearance, which could be occurred in the relatedart described above, can be avoided, and generation of scratch caused bystarting rotation in the tightly sticked state can be positivelyprevented.

Since the ball 51 is formed of porous ceramic that can impregnate oil,lubricity can be further improved.

In the spindle motor disclosed in Japanese Unexamined Patent ApplicationPublication No. 11-311245, as shown in FIG. 1 and the paragraphs [0016]to [0017] of the same publication, in a state in which the free end ofthe shaft body touches the closed end surface (upper side in the figure)of the cylindrical member, a gap is formed between the end surface ofthe cylindrical member on the side of the opening and the upper surfaceof the support (lower side in the figure), so that the free end of theshaft body is configured into a curved surface. In this spindle motor,the curved surface (projecting portion) is formed of the same materialas the cylindrical member. Therefore, manufacturing of the shaft body isconstrained, which results in lowering of versatility correspondingly.On the other hand, in this embodiment, since the projection (ball 51) isprovided separately from the member on which the projection is provided(shaft boy 12 a), the member on which the projection is provided (shaftbody 12 a) may be used widely to various types of the motor, therebyimproving productivity correspondingly.

In the embodiment described above, there is shown an example in whichthe ball 51 is provided on the end surface 12 b of the shaft body 12 a.Alternatively, as shown in FIG. 5, the ball 51 may be press-fitted tothe end surface 10 b of the annular body 10 (second embodiment). Thesecond embodiment corresponds to the third aspect of the presentinvention. In the second embodiment, the height h of the ball 51(dimension of the annular body 10 projecting from the end surface 10 b)is specifically determined as follows.

The distance G22, the distance G32, and the distance G02 shown in FIG. 5are determined as follows, and the height h1 of the ball 51 isdetermined so that the sum of the distance G22 and the distance G32 isequal to the distance G02; (G22+G32=G02).

(1) The distance G22: The axial distance between the end surface 10 b ofthe annular body 10 and the upper surface 11 a of the counter plate 11when the tip portion of the ball 51 touches the upper surface 11 a ofthe counter plate 11 with the shaft 12 remained at rest. FIG. 5 is across section taken when the shaft 12 is being rotated, and the distanceG22 shown in FIG. 5 is marked just for the sake of convenience.

(2) The distance G32: The axial distance between the tip portion of theball 51 and the upper surface 11 a of the counter plate 11 when theshaft 12 is rotated at a specified rotational speed.

(3) The distance G02: The axial distance between the end surface 10 b ofthe annular body 10 and the upper surface 11 a of the counter plate 11when the shaft 12 is rotated at a specified rotational speed.

In the second embodiment, when the shaft 12 is remained at rest, theball 51 abuts against the upper surface 11 a of the counter plate 11,and as in the first embodiment, the end surface 10 b of the annular body10 is brought into a state of being raised from the upper surface 11 aof the counter plate 11, so that the situation in which the end surface10 b of the annular body 10 and the upper surface 11 a of the counterplate 11 are brought into almost fully touch each other can be avoided.Therefore, a fluid circularity blocking action that could be occurred inthe related art can be avoided and generation of scratch caused bystarting rotation in the tightly sticked state can be positivelyprevented.

In the first and second embodiment, there is shown an example in whichthe ball 51 is provided on the shaft 12 side (the shaft body 12 a or theannular body 10). Alternatively, as shown in FIGS. 6 to 8, the ball 51may be press-fitted to the portion 11 b on the upper surface 11 a of thecounter plate 11 facing toward the end surface 12 b of the shaft body 12a (the surface on the stationary portion facing toward the shaft body)(third embodiment). The third embodiment corresponds to the fifth aspectof the present invention. In the third embodiment the height h of theball 51 (dimension projecting from the upper surface 11 a of the counterplate 11) is determined to be larger than the dimension from the endsurface 12 b of the shaft body 12 a to the end 10 b of the annular body10, and specifically it is determined as follows.

The distance G23, the distance G33, and the distance G03 shown in FIG. 8are determined as follows, and the height h of the ball 51 is determinedso that the sum of the distance G23 and the distance G33is equal to thedistance G03; (G23+G33=G03).

(1) The distance G23: The axial distance between the end surface 10 b ofthe annular body 10 and the upper surface 11 a of the counter plate 11when the tip portion of the bail 51 touches the end surface 12 b of theshaft body 12 a with the shaft 12 remained at rest. FIG. 8 is a crosssection taken when the 12 is being rotated, and the distance G23 shownin FIG. 8 is marked just for the sake of convenience.

(2) The distance G33: The axial distance between the tip portion of theball 51 and the end surface 12 b of the shaft body 12 a when the shaft12 is rotated at a specified rotational speed.

(3) The distance G03: The axial distance between the end surface 12 b ofthe shaft body 12 a and the upper surface 11 a of the counter plate 11when the shaft 12 is rotated at a specified rotational speed.

In the third embodiment, when the shaft 12 is remained at rest, the ball51 abuts against the end surface 12 b of the shaft body 12 a, and as inthe first embodiment, the end surface 10 b of the annular body 10 isbrought into a state of being raised from the upper surface 11 a of thecounter plate 11, so that the situation in which the end surface 10 b ofthe annular body 10 and the upper surface 11 a of the counter plate 11are brought into almost fully touch each other can be avoided.Therefore, a fluid circularity blocking action that could be occurred inthe related art can be avoided and generation of scratch caused bystarting rotation in the tightly sticked state can be positivelyprevented.

In the third embodiment, there is shown an example in which the ball 51is press-fitted into the portion on the surface 11 b of the counterplate facing toward the shaft body (the portion on the surface of thestationary portion facing toward the shaft body). Alternatively, asshown in FIG. 9, the ball 51 may be press-fitted to the portion 11 c onthe upper surface 11 a of the counter plate 11 facing toward the endsurface 10 b of the annular body 10 (the portion on the surface of thestationary portion facing toward the annular body) (fourth embodiment).The fourth embodiment corresponds to the fourth aspect of the presentinvention. In the fourth embodiment, the height h of the ball 51(dimension projecting from the upper surface 11 a of the counter plate11) is determined as follows.

The distance G24, the distance G34, and the distance G04 shown in FIG. 9are determined as follows, and the height h1 of the ball 51 isdetermined so that the sum of the distance G24 and the distance G34 isequal to the distance G04; (G24+G34=G04).

(1) The distance G24: The axial distance between the end surface 10 b ofthe annular body 10 and the upper surface 11 a of the counter plate 11when the tip portion of the ball 51 touches the surface 10 b of theannular body 10 with the shaft 12 remained at rest. FIG. 9 is a crosssection taken when the shaft 12 is being rotated, and the distance G24shown in FIG. 10 is marked just for the sake of convenience.

(2) The distance G34: The axial distance between the tip portion of theball 51 and the end surface 10 b of the annular body 10 when the shaft12 is rotated at a specified rotational speed.

(3) The distance G04: The axial distance between the end surface 10 b ofthe annular body 10 and the upper surface 11 a of the counter plate 11when the shaft 12 is rotated at a specified rotational speed.

In the fourth embodiment, when the shaft 12 is remained at rest, theball 51 abuts against the end surface 10 b of the annular body 10, andas in the first embodiment, the end surface 10 b of the annular body 10is brought into a state of being raised from the upper surface 11 a ofthe counter plate 11, so that the situation in which the end surface 10b of the annular body 10 and the upper surface 11 a of the counter plate11 are brought into almost fully touch each other can be avoided.Therefore, a fluid circularity blocking action that could be occurred inthe related art can be avoided and generation of caused by startingrotation in the tightly sticked state can be positively prevented.

In the first to fourth embodiments, there is shown an example in whichthe shaft 12 constructed of the shaft body 12 and the annular body 10 isused. Alternatively, as shown in FIG. 10, it is also possible to use ashaft that is not provided with the annular body 10 hereinafter referredto as a single shaft for the sake of convenience) 12T, and the ball 51is press-fitted into the end surface 12T1 of the single shaft 12T (fifthembodiment). The fifth embodiment corresponds to the first aspect of thepresent invention. In the fifth embodiment, the height h1 of the ball 51(dimension of the single shaft 12T projecting from the end surface 12T1)is determined as follows.

The distance G25, the distance G35, and the distance G05 shown in FIG.10 are determined as follows, and the height h1 of the ball 51 isdetermined so that the sum of the distance G25 and the distance G35 isequal to the distance G05; (G25+G35=G05).

(1) The distance G25: The axial distance between the end surface 12T1 ofthe shingle shaft 12T and the upper surface 11 a of the counter plate 11when the tip portion of the ball 51 touches the upper surface 11 a ofthe counter plate 11 with the shaft 12 remained at rest. FIG. 10 is across section taken when the shaft 12 is being rotated, and the distanceG25 shown in FIG. 9 is marked just for the sake of convenience.

(2) The distance G35: The axial distance between the tip portion of theball 51 and the upper surface 11 a of the counter plate 11 when thesingle shaft 12T is rotated at a specified rotational speed.

(3) The distance G05: The axial distance between the end surface 12T1 ofthe single shaft 12T and the upper surface 11 a of the counter plate 11when the single shaft 12T is rotated at a specified rotational speed.

In the fifth embodiment, when the single shaft 12T is remained at rest,the ball 51 abuts against the upper surface 11 a of the counter plate11, and as in the first embodiment, the end surface 12T1 of the singleshaft 12T is brought into a state of being raised from the upper surface11 a of the counter plate 11, so that the situation in which the endsurface 12T1 of the single shaft 12T1 and the upper surface 11 a of thecounter plate 11 are brought into almost fully touch other can beavoided.

Therefore, a fluid circularity blocking action that could be occurred inthe related art can be avoided. Therefore, a fluid circularity blockingaction that could be occurred in the related art can be avoided andgeneration of scratch caused by starting rotation in the tightly stickedstate can be positively prevented.

In the fifth embodiment, there is shown an example in which the ball 51is press-fitted to the end 12T1 of the single shaft 12T. Alternatively,it is also possible press-fit the ball 51 into the upper surface 11 a ofthe counter plate 11 so that the portion on the tip side projects fromthe upper surface 11 a of the counter plate 11 (corresponding to theinvention according to the claim 1 or claim 2).

In each embodiment described above, there is shown an example in whichthe ball 51 is press-fitted into the member on which the ball 51 is tobe provided (shaft body 12 a, the annular body 10, or the counter plate11). However, it is also possible to fix the ball 51 on the member onwhich the ball 51 is to be provided (shaft body 12 a, the annular body10 or the counter plate 11) with fixing means such as adhesives. In thiscase, the fixing means such as adhesives should be compatible with thefluid.

In each of the embodiment described above, there is shown an example inwhich the projection is a ball 51 formed of ceramic. Alternatively, itmay be a steel ball.

The projection is not limited to the spherical shape (ball 51) describedin the above-described embodiments, but it may be a conical projectionas shown in FIG. 11, or may be other shapes such as a shaft shape andtapered shape. When the tapered shape is employed, the tip portion ispreferably formed into a convex curved shape so as not to set down themated surface that touches it.

In addition, in the embodiments described above, there is shown anexample in which the projection (ball 51) is formed separately from themember on which the projection (ball 51) is provided (shaft body 12 a,annular body 10 or the counter plate 11). Alternatively, the projectionmay be formed integrally with the member on which the projection isprovided (shaft body 12 a, annular body 10 or the counter plate 11). Forexample, as shown in FIG. 12, it is also possible to form the projection52 of conical shape on the upper surface 11 a of the counter plate 11.

In the embodiments described above, there are shown examples in whichthe ball 51 is press-fitted into the member (shaft body 12 a, annularbody 10 or counter plate 11) or fixed thereon with the fixing means suchas adhesives. As an alternative thereto, as shown in FIGS. 13-19, theprojection may be a member made of a high hardness material formed bythe sputtering (corresponding to claims 10 to 12).

In the sixth embodiment, as shown in FIG. 13, a single disk-likeprojection 55 is provided at the center of the end surface 12 b of theshaft body 12 a. The diameter and the height h1 of the projection 55 is0.5 mm to 5 mm and 2 μm, respectively. The projection 55 is composed ofa base member 56 containing silicon or chromium as a main component andbeing 0.5 μm in its height and a secondary member made of a highhardness material 57 (hereinafter a secondary member 57) placed thereonand being 1.5 μm in its height and both of the members are formed by thesputtering. The secondary member 57 is made of DLC, which is formed bybeing crystallized in an atmosphere of hydrogen or methane,characterized in that the hardness or smoothness thereof is moresuperior to amorphous carbon (crystal body made by which carbon iscrystallized in a vacuum).

As described above, the height h1 of the projection 55 is determined tobe 2 μm and the tip portion thereof is made to be higher than the endsurface 10 b of the annular body 10. To be specific, the ball 51 asshown in FIG. 4 is replaced by the projection 55, and each specificmeasurement is determined as same as the first embodiment. And, themeasurement ht projected from the end surface 12 b of the shaft body 12a (hereinafter projection measurement of the projection 55) isdetermined in a state that the height h1 of the projection 55 is set tobe 2 μm. That is, when considering the projection measurement ht or theheight h1 of the projection 55 (2 μm), the sum of the distance G2 andthe distance G3 is equal to the distance G0 (G2+G3=G0).

In the sixth embodiment thus constructed, when the shaft 12 remains atrest, the projection 55 abuts against the upper surface 11 a of thecounter plate 11, and the end surface 10 b of the annular body 10 isbrought into a state of being raised from the upper surface 11 a of thecounter plate 11. Moreover, since the shaft 12 is sufficiently raised toa specific level and in a quick motion, problems occurred in prior artscan be effectively prevented. That is, an adhesion occurred in a coheredstate or a fluid circularity blocking action due to a small aperture canbe prevented. Moreover, scratches caused when a rotor is started torotate in the cohered state can be prevented in a certain manner.

In addition, durability is improved due to that the secondary member 57of the projection 55 is made by DLC which is characteristically superiorin a high hardness and a surface smoothness. In this case, because thesputtering is not a complicated method, obtaining of the projection 55is easy. For example, by forming an aperture on a stainless mask andconducting the sputtering thereover, the projection can be formed.Alternatively, in case that a plurality of projections are formed at atime, apertures corresponding to the projections should be made on themask, then a plurality of projections can be formed by conducting onlyone sputtering. In addition, a conical or a hemisphere projection can beformed by adjusting the shape of the mask.

Further, the projection 55 provided at the end surface 12 b of the shaftbody 12 a comprises the base member 56 containing silicon or chromium asa main component and secondary member 57 made of a high hardnessmaterial placed thereon, and both of the members are formed by thesputtering. That is, since the base member 56 is placed between the endsurface 12 b of the shaft body 12 a and the secondary member 57, thesecondary member 57 and the end surface 12 b can be made a certainattachment.

Because the projection 55 is provided at the center of the end surface12 b of the shaft body 12 a, a staring torque can be reduced. However,the portion at where the projection 55 is provided is not limited to thecenter of the end surface 12 b of the shaft body 12 a. Instead, theprojection 55 can be provided at any point as long as that is at the endshaft 12 b of the shaft body 12 a. Alternatively, the projection 55 canbe provided in a plural number. In this case a plurality of theprojections 55 should be provided in such a manner that a load of theshaft 12 is most effectively supported.

Furthermore, since the projection 55 abuts against the upper surface 11a of the counter plate 11 giving more gap between the upper surface 11 aof the counter plate 11 and the end surface 12 b of the shaft body 12 a,more amount of oil can be filled and reserved therein.

Still further, in the sixth embodiment there is shown example in whichthe height h1 of the projection 55 is set to be 2 μm, but this is notlimited thereto. Instead, the height h1 can be set within the range from0.02 μm to 5 μm, and this can be also applied to the seventh to twelfthembodiments described hereinafter.

And, in the sixth embodiment there is shown example in which thesecondary member 57 of the projection 55 is made of DLC, but this is notlimited thereto. Instead, the secondary member 57 can be made ofamorphous carbon, and this can be applied to the seventh to twelfthembodiments described hereinafter.

Furthermore, in the sixth embodiment there is shown example in which theprojection 55 comprises the base member 56 being 0.5 μm in its heightand the secondary member 57 1.5 μm in its height, but this is notlimited thereto. Instead, the projection 55 can be composed only of thesecondary member 57 being 2.0 μm in its height without providing any ofthe base member 56. In this case the height of the secondary member 57(or the projection 55) is not limited to 2.0 μm but can be set withinthe range from 0.02 μm to 5 μm (corresponding to claim 10), and this canbe applied to the seventh to twelfth embodiments described hereinafter.

In the sixth embodiment (FIG. 13) there is also shown example in whichthe projection 55 is provided on the end surface 12 b of the shaft body12 a, but this is not limited thereto. Instead, in the seventhembodiment as shown in FIG. 14, the projection 55 is provided on the endsurface 10 b of the annular body 10. In this seventh embodiment theheight h1 of the projection 55 (projection measurement from the endsurface 10 b of the annular body 10) is set to be 2 μm. Moreover, in theseventh embodiment each measurement G 22, G 32 and G 02 is determined assame as the case of the second embodiment by replacing the ball 51 withthe projection 55. That is, the sum of the distance G 22 and thedistance G 32 is equal to the distance G 02 (G22+G32=G02).

In the sixth and seventh embodiment there is shown example in which theprojection 55 is provided on the side of the shaft 12 (shaft body 12 aor annular body 10), but this is not limited thereto. Instead, as shownin FIG. 15 (corresponding to the eighth embodiment), the projection 55can be provided on the surface 11 b of the counter plate 11 facing theend surface 12 b of the shaft body 12 a. In the eighth embodiment theheight h1 of the projection 55 (projection measurement from the uppersurface 11 a of the counter plate 11) is set to be 2 μm. Moreover, eachmeasurement of G 23, G 33 and G 03 as shown in FIG. 15 is determined assame as the case of the third embodiment by replacing the ball 51 withthe projection 55. That is, the sum of the distance G 23 and thedistance G 33 is equal to the distance G 03 (G 23+G 33=G 03).

In the above eighth embodiment the projection 55 is provided on thesurface 11 b of the counter plate 11, but this is not limited thereto.Instead, as shown in FIG. 16 (corresponding to the ninth embodiment),the projection 55 can be provided on the portion 11 c of the counterplate 11 facing the end surface 10 b of the annular body 10. In theninth embodiment the height h1 of the projection 55 (projectionmeasurement from the upper surface 11 a of the counter plate 11) is setto be 2 μm. Moreover, each measurement of G 24, G 34 and G 04 as shownin FIG. 16 is determined as same as the case of the forth embodiment byreplacing the ball 51 with the projection 55. That is, the sum of thedistance G 24 and the distance G 34 is equal to the distance G 04(G24+G34=G04).

In the sixth to ninth embodiments that is shown example in which theshaft 12 is composed of the shaft body 12 a and the annular body 10, butthis is not limited thereto. Instead, as shown in FIG. 17 (correspondingto the tenth embodiment) the projection 55 can be provided on the endsurface 12T1 of the singe shaft 12T meaning the shaft not having theannular body 10. In the tenth embodiment the height h1 of the projection55 (projection measurement from the end surface 12T1 of the single shaft12T) is set to be 2 μm. Moreover, each measurement of G 25, G 35 and G05 as shown in FIG. 17 is determined as same as the case of the fifthembodiment by replacing the ball 51 with the projection 55. That is, thesum of the distance G 25 and the distance G 35 is equal to the distanceG05(G25+G35=G05).

Further, in the sixth to tenth embodiments there is shown example inwhich the projection 55 is plate-like shape, but this is not limitedthereto. Instead, as shown in FIG. 18, the projection 55 can be conicalshape or hemisphere shape as shown in FIG. 18 (corresponding to theeleventh embodiment) and FIG. 19 (corresponding to the twelfthembodiment), respectively.

According to the present invention, when the rotating member is at rest,a gap is generated between the opposing generally flat end surfaces ofthe fluid dynamic bearing by the abutment of the projection, and one ofthese opposing end surfaces is brought into a state of being raised fromthe other end surface, so that the situation in which both of the endsurfaces are brought into almost fully touch each other can be avoided.Therefore, a fluid circularity blocking action that could be occurred inthe related art can be avoided and generation of scratch caused bystarting rotation in the tightly sticked state can be positivelyprevented.

What is claimed is:
 1. A motor having a rotating member supported on astationary portion via a fluid dynamic bearing supporting both of athrust load and a radial load, comprising: one or more projectionsprovided on one of the opposing generally flat surface at the end of theshaft to the fluid dynamic bearing each as a separate unit;characterized in that said one of more projections are capable ofabutting against the other surface when said rotating member is at rest.2. A motor as set forth in claim 1, characterized in that said one ofthe surfaces is an end surface of the shaft provided on said rotatingmember and said the other one of the surface is said portion on thesurface of the stationary portion facing toward the end surface of theshaft, or said one of the surfaces is said portion on the surface of thestationary portion facing toward the end surface of the shaft and theother one of the surfaces is an end surface of the shaft.
 3. A motorhaving a shaft fitted with an annular body on one end of the shaft bodyand a rotating member supported on the stationary portion via a fluiddynamic bearing for supporting both of a thrust load and a radial load,characterized in that one or more projections are provided on the endsurface of said shaft body each as a separate unit, and; in that saidprojection is provided in such a manner that the tip portion thereofcomes to the position higher than the end surface of the annular body.4. A motor as set forth in claim 1, to characterized in that saidprojection is press-fitted to the member on which said projection is tobe provided.
 5. A motor as set forth in claim 1, to claim 7,characterized in that said projection has a spherical shape.
 6. A motoras set forth in claim 1, characterized in that said projection is formedof ceramic.
 7. A motor as set forth in claim 1, characterized in thatsaid projection is a member made of a high hardness material formed by asputtering.
 8. A motor as set forth in claim 1, characterized in thatsaid projection is formed of a base member containing silicon orchromium as a main component and a secondary member made of a highhardness material placed thereon, and both of said members are formed bythe sputtering.
 9. A motor as set forth in claim 7, characterized inthat said member made of a high hardness material is amorphous carbon orDiamond-like Carbon.
 10. A motor having a rotating member with a shaftthat is supported on a stationary portion via a fluid dynamic bearingfor supporting both of a thrust load and a radial load, comprising: atleast one projection on one of a first surface of the shaft of therotating member and a second surface of the stationary portion opposingthe first surface, wherein the at least one projection abuts against theother of the first and second surfaces when the rotating member is atrest.